Human T-cell leukemia retrovirus-Tax protein is a repressor of nuclear receptor signaling

The Tax oncoprotein promotes cellular transformation and is associated with the pathogenesis of adult T-cell leukemia. Tax expression activates transcription via the cAMP enhancer binding protein/activating transcription factor (CREB/ATF) and NF-kappaB pathways. In contrast to its positive action, here we demonstrate that Tax is a potent repressor of steroid and retinoid receptor transcription. The Tax protein becomes localized in the promyelocytic (PML) oncogenic domain, and unexpectedly, expression of the PML protein reverses Tax-induced repression. These results suggest that PML and Tax may act in opposing manners to influence nuclear receptor transcription and human T-cell leukemia retrovirus pathogenesis.

Unique forms of human and mouse nuclear receptor corepressor SMRT

Nuclear hormone receptors have been shown to repress transcription in the absence of ligand. This repression is mediated by a corepressor complex that contains the Sin3A protein and histone deacetylases (HDAC1 and 2). Studies by several groups demonstrate that this complex is recruited to nuclear receptors through the highly related corepressors SMRT (silencing mediator of retinoid acid and thyroid hormone receptor) and N-CoR (nuclear receptor corepressor). We describe here the cloning, characterization, and chromosomal mapping of forms of human and mouse SMRT that includes a 1,000-aa extension, which reveals striking homology to the amino terminus of N-CoR. Structure and function studies of wild-type and natural splicing variants suggest the presence of 3-4 amino terminal domains that repress in a cooperative as well as mechanistically distinct fashion.

Modulation of CREB binding protein function by the promyelocytic (PML) oncoprotein suggests a role for nuclear bodies in hormone signaling

Disaggregation of the spherical nuclear bodies termed promyelocytic (PML) oncogenic domains (PODs) is a characteristic of acute promyelocytic leukemia. Here, we demonstrate that the cAMP enhancer binding protein (CREB)-binding protein (CBP) associates with PML in vitro and is recruited to the PODs in vivo. Through its association with CBP, wild-type PML dramatically stimulates nuclear receptor transcriptional activity. These results demonstrate that a fraction of CBP is compartmentalized to the POD through its association with PML and thus suggest that PML and other POD-associated proteins may play an unexpectedly broad role in aspects of transcriptional regulation and human disease.

A viral mechanism for inhibition of p300 and PCAF acetyltransferase activity

Nucleosomal histone modification is believed to be a critical step in the activation of RNA polymerase II-dependent transcription. p300/CBP and PCAF histone acetyltransferases (HATs) are coactivators for several transcription factors, including nuclear hormone receptors, p53, and Stat1alpha, and participate in transcription by forming an activation complex and by promoting histone acetylation. The adenoviral E1A oncoprotein represses transcriptional signaling by binding to p300/CBP and displacing PCAF and p/CIP proteins from the complex. Here, we show that E1A directly represses the HAT activity of both p300/CBP and PCAF in vitro and p300-dependent transcription in vivo. Additionally, E1A inhibits nucleosomal histone modifications by the PCAF complex and blocks p53 acetylation. These results demonstrate the modulation of HAT activity as a novel mechanism of transcriptional regulation.

Vimentin and lipid metabolism

Vimentin IFs form close associations with the lipid droplets that are characteristic of adipose and steroidogenic cells. There is good evidence that changes in vimentin expression or organization can alter the metabolism of specific lipid components in cultured preadipose and adrenal cell lines. However, the effect of vimentin on triglyceride stability that is observed in preadipose cells is not obviously reflected in adrenal cells or fibroblasts. Conversely, an effect of vimentin on the metabolism of lipoprotein-derived cholesterol observed in adrenal cells is not apparent in preadipose cells. While the complexity of the phenotypes observed in these cells might be associated with cell-type-specific differences in the metabolism of triglycerides or lipoprotein-derived cholesterol, these studies have not yet revealed a general role of vimentin in lipid metabolism that would indicate a common mechanism in all cell types. A key issue that needs to be addressed is whether the effect of vimentin IFs on the stability of triglycerides or the trafficking of GSLs and lysosomal cholesterol is due to a direct participation of vimentin IFs in some aspect of these processes, or perhaps reflects an indirect response of the lipid metabolism of these cells to an effect of vimentin on some other cellular process.

An essential role for retinoid receptors RARbeta and RXRgamma in long-term potentiation and depression

Hippocampal long-term potentiation (LTP) and long-term depression (LTD) are the most widely studied forms of synaptic plasticity thought to underlie spatial learning and memory. We report here that RARbeta deficiency in mice virtually eliminates hippocampal CA1 LTP and LTD. It also results in substantial performance deficits in spatial learning and memory tasks. Surprisingly, RXRgamma null mice exhibit a distinct phenotype in which LTD is lost whereas LTP is normal. Thus, while retinoid receptors contribute to both LTP and LTD, they do so in different ways. These findings not only genetically uncouple LTP and LTD but also reveal a novel and unexpected role for vitamin A in higher cognitive functions.

Cisplatin induced intermediate filament reorganization and altered mitochondrial function in 3T3 cells and drug-sensitive and -resistant Walker 256 cells

Cisplatin has acute but reversible effects on the organization of the intermediate filament component of the cytoskeleton as well as the mitochondrial function of cultured 3T3 cells. These effects do not involve major changes in total cell or cytoskeletal protein synthesis and appear to be distinct from the long-term cytotoxicity produced by the drug. Cells treated with similar concentrations of second-generation platinum compounds, which have reduced nephrotoxic effects in vivo, do not exhibit alterations in intermediate filament organization nor mitochondrial rhodamine 123 fluorescence. Similar studies with cisplatin-sensitive and -resistant lines of rat Walker 256 cells indicated that the drug-induced intermediate filament collapse and decreased mitochondrial rhodamine 123 fluorescence correlated with the susceptibility of these cells to the lethal effects of cisplatin.

The LAZ3(BCL-6) oncoprotein recruits a SMRT/mSIN3A/histone deacetylase containing complex to mediate transcriptional repression

Recent works demonstrated that some transcriptional repressors recruit histone deacetylases (HDACs) either through direct interaction, or as a member of a multisubunit repressing complex containing other components referred to as corepressors. For instance, the bHLH-Zip transcriptional repressors MAD/MXI recruit HDACs together with the mSIN3 corepressors, whereas unliganded nuclear receptors contact another corepressor, SMRT (or its relative N-CoR), which, in turn, associates with both mSIN3 and HDACs to form the repressor complex. Recently, we reported that SMRT also directly associates with LAZ3(BCL-6), a POZ/Zn finger transcriptional repressor involvedin the pathogenesis of non-Hodgkin lymphomas. However, whether LAZ3 recruits the HDACs-containing repression complex is currently unknown. We report here that LAZ3 associates with corepressor mSIN3A both in vivo and in vitro , and found that a central region, which harbours autonomous repression activity, is mainly responsible for this interaction. Conversely, the N-terminal half of mSIN3A is both necessary and sufficient to bind LAZ3. Moreover, we show that LAZ3 also interacts with an HDAC (HDAC-1) through its POZ domain in vitro while the immunoprecipitation of LAZ3 results in the coretention of an endogenous HDAC activity in vivo . Finally, inhibitors of HDACs significantly reduce the LAZ3-mediated repression. Taken together, we conclude that LAZ3 recruits a repressing complex containing SMRT, mSIN3A and a HDAC, and that its full repressing potential on transcription requires HDACs activity. Our results identify HDACs as molecular targets of LAZ3 oncogene and further strengthen the connection between aberrant chromatin acetylation and human cancers.

SXR, a novel steroid and xenobiotic-sensing nuclear receptor

An important requirement for physiologic homeostasis is the detoxification and removal of endogenous hormones and xenobiotic compounds with biological activity. Much of the detoxification is performed by cytochrome P-450 enzymes, many of which have broad substrate specificity and are inducible by hundreds of different compounds, including steroids. The ingestion of dietary steroids and lipids induces the same enzymes; therefore, they would appear to be integrated into a coordinated metabolic pathway. Instead of possessing hundreds of receptors, one for each inducing compound, we propose the existence of a few broad specificity, low-affinity sensing receptors that would monitor aggregate levels of inducers to trigger production of metabolizing enzymes. In support of this model, we have isolated a novel nuclear receptor, termed the steroid and xenobiotic receptor (SXR), which activates transcription in response to a diversity of natural and synthetic compounds. SXR forms a heterodimer with RXR that can bind to and induce transcription from response elements present in steroid-inducible cytochrome P-450 genes and is expressed in tissues in which these catabolic enzymes are expressed. These results strongly support the steroid sensor hypothesis and suggest that broad specificity sensing receptors may represent a novel branch of the nuclear receptor superfamily.

Androstane metabolites bind to and deactivate the nuclear receptor CAR-beta

The orphan receptor CAR-beta binds DNA as a heterodimer with the retinoid-X receptor and activates gene transcription in a constitutive manner. Here we show that, in contrast to the classical nuclear receptors, the constitutive activity of CAR-beta results from a ligand-independent recruitment of transcriptional co-activators. While searching for potential ligands of CAR-beta, we found that the steroids androstanol and androstenol inhibit the constitutive activity of CAR-beta. This effect is stereospecific: only 3alpha-hydroxy, 5alpha-reduced androstanes are active. These androstanes do not interfere with heterodimerization or DNA binding of CAR-beta; instead, they promote co-activator release from the ligand-binding domain. These androstane ligands are examples of naturally occurring inverse agonists that reverse transcriptional activation by nuclear receptors. CAR-beta (constitutive androstane receptor-beta), therefore, defines an unanticipated steroidal signalling pathway that functions in a manner opposite to that of the conventional nuclear receptor pathways.

Activators of the nuclear receptor PPARgamma enhance colon polyp formation

A high-fat diet increases the risk of colon, breast and prostate cancer. The molecular mechanism by which dietary lipids promote tumorigenesis is unknown. Their effects may be mediated at least in part by the peroxisome proliferator-activated receptors (PPARs). These ligand-activated nuclear receptors modulate gene expression in response to fatty acids, lipid-derived metabolites and antidiabetic drugs. To explore the role of the PPARs in diet-induced carcinogenesis, we treated mice predisposed to intestinal neoplasia with a synthetic PPARgamma ligand. Reflecting the pattern of expression of PPARgamma in the gastrointestinal tract, treated mice developed a considerably greater number of polyps in the colon but not in the small intestine, indicating that PPARgamma activation may provide a molecular link between a high-fat diet and increased risk of colorectal cancer.

Effects of an asthma management program on the asthmatic member: patient-centered results of a 2-year study in a managed care organization

OBJECTIVE

To report the results of a 2-year pilot program of asthma education based on National Heart, Lung, and Blood Institute treatment guidelines.

PATIENTS AND METHODS

Asthmatic members (n = 6698) of a managed care organization received education about their condition directly or through their primary care physician. Medical and pharmacy administrative claims data were reviewed to measure acute asthma events and prescribed therapies in the first (the baseline) and second years of the study. The claims data were augmented by member surveys from a stratified random sample of 2734 asthmatic patients who were members (6 years of age or older) in the baseline year.

RESULTS

Compared with the first year, asthmatic members received fewer inpatient services and the proportion of asthmatic members prescribed oral inhaled corticosteroids increased 30% in the second year. Health-related quality of life, measured with validated general and disease-specific instruments; satisfaction with the quality of care; exposure to patient education; knowledge of the disease; and member's confidence in their ability to manage their disease showed statistically significant improvements during the follow-up year of the program for both adult and child asthmatic members.

CONCLUSION

For asthmatic members of this health plan, a comprehensive asthma health management program improved processes of care and outcomes.

Pitx2 determines left-right asymmetry of internal organs in vertebrates

The handedness of visceral organs is conserved among vertebrates and is regulated by asymmetric signals relayed by molecules such as Shh, Nodal and activin. The gene Pitx2 is expressed in the left lateral plate mesoderm and, subsequently, in the left heart and gut of mouse, chick and Xenopus embryos. Misexpression of Shh and Nodal induces Pitx2 expression, whereas inhibition of activin signalling blocks it. Misexpression of Pitx2 alters the relative position of organs and the direction of body rotation in chick and Xenopus embryos. Changes in Pitx2 expression are evident in mouse mutants with laterality defects. Thus, Pitx2 seems to serve as a critical downstream transcription target that mediates left-right asymmetry in vertebrates.

A histone deacetylase corepressor complex regulates the Notch signal transduction pathway

The Delta-Notch signal transduction pathway has widespread roles in animal development in which it appears to control cell fate. CBF1/RBP-Jkappa, the mammalian homolog of Drosophila Suppressor of Hairless [Su(H)], switches from a transcriptional repressor to an activator upon Notch activation. The mechanism whereby Notch regulates this switch is not clear. In this report we show that prior to induction CBF1/RBP-Jkappa interacts with a corepressor complex containing SMRT (silencing mediator of retinoid and thyroid hormone receptors) and the histone deacetylase HDAC-1. This complex binds via the CBF1 repression domain, and mutants defective in repression fail to interact with the complex. Activation by Notch disrupts the formation of the repressor complex, thus establishing a molecular basis for the Notch switch. Finally, ESR-1, a Xenopus gene activated by Notch and X-Su(H), is induced in animal caps treated with TSA, an inhibitor of HDAC-1. The functional role for the SMRT/HDAC-1 complex in CBF1/RBP-Jkappa regulation reveals a novel genetic switch in which extracellular ligands control the status of critical nuclear cofactor complexes.

Preventive pharmacologic therapy among asthmatics: five years after publication of guidelines

BACKGROUND

Guidelines from the National Heart, Lung, and Blood Institute first published in 1991 have recommended anti-inflammatory (AI) agents as a first-line therapy and the bronchodilator as an acute reliever of symptoms.

OBJECTIVE

To examine the current usage of anti-inflammatory steroids (inhaled corticosteroids, Cromolyn, systemic steroids) and bronchodilators and compare them with the national guidelines. The relationship between preventive AI usage and the characteristics of the asthma patients and their providers was also examined.

METHODS

Cross-sectional survey data linked with 6-month pharmacy claims of asthmatic members at an HMO in California.

RESULTS

AI usage increased with current severity (mild, 36.9%; moderate, 47.3%; and severe, 56.8%), though a large percentage are not receiving this emphasized treatment. Bronchodilators were used at a higher rate and 24% of asthmatics relied solely on bronchodilators. Use of bronchodilators without AI (BWAI) was present at all severity levels (mild, 19.5%; moderate, 24.6%; and severe, 24.7%). Advancing age, increasing severity, care by an asthma specialist, and not smoking increased the likelihood of using AIs. Increasing severity, longer duration of asthma, smoking, younger age group, care by a generalist, and no chronic bronchitis increased the likelihood of BWAI.

CONCLUSIONS

These results suggest that there is a low level of AI usage despite emphasis in guidelines. Current asthma management in a community-based setting depicts a significant underutilization of long-term control agents and, conversely, an overutilization of symptom relief agents compared with guidelines published 5 years ago. Actively involving patients in the guideline dissemination process, rather than just the medical community, may increase preventive medication usage.

Pharmacologic treatment of cognition in Alzheimer's dementia

Much of the treatment research and development for Alzheimer's disease (AD) in recent years has been based on the cholinergic hypothesis. Cholinesterase inhibition has been shown to improve the symptoms of mild to moderate AD. Two cholinesterase inhibitors (CIs) are now available and two more may be available shortly. Free radical inhibitors, estrogen, and anti-inflammatory drugs may also delay the onset and slow progression of AD. Combination therapies employing CIs and these other drugs may prove successful in the future.

Begging as graded signals of need for food in young ring-billed gulls

Recent models suggest that begging vocalizations are honest signals communicating a chick's nutritional needs to its parents. We investigated the effects on begging of short-term food deprivation ('hunger') and long-term reduction in body condition under controlled laboratory conditions in ring-billed gulls, Larus delawarensis. We tested two condition groups (high: fed to satiation; low: fed 75% wet mass of high-condition diet) at three levels of short-term food deprivation (1, 4 and 12 h). Begging call rate, intensity and peck rate were significantly greater in the low-condition chicks. Begging in both high- and low-condition groups increased with short-term deprivation, tending to asymptotic levels by 12 h of deprivation. Overall level of begging was graded according to both short- and long-term need for food, with steep slopes at the beginning of the begging curves providing a strong basis for parental discrimination of signalling level. The system appears to agree with the design requirements of a homeostatic control system, and with predictions of current game-theoretic models of honest signalling. Possible effects of sibling competition and parent-offspring conflict are discussed. These issues require further study under natural conditions in this species. Copyright 1998 The Association for the Study of Animal Behaviour.

Synthesis and accumulation of a receptor regulatory protein associated with lipid droplet accumulation in 3T3-L1 cells

Synthesis and accumulation of the recently identified prostaglandin F2alpha receptor regulatory protein (FPRP) was found to correlate closely with lipid droplet accumulation by 3T3-L1 preadipose cells. FPRP, a transmembrane glycoprotein, has been shown to regulate the binding of ligand to certain seven-transmembrane receptors. Anti-FPRP immunohistochemistry, Western blotting, and metabolic labeling/immunoprecipitation experiments demonstrated that FPRP was not detectable in undifferentiated 3T3-L1 cells. Interestingly, low levels of FPRP mRNA were detected in the undifferentiated 3T3-L1 cells. After induction of adipose differentiation, FPRP mRNA increased approximately 3 fold whereas FPRP synthesis increased approximately 50 fold. Differentiation induction with either dexamethasone/insulin/isobutylmethylxanthine or the thiazolidinedione derivative ADD 4743 were both effective at inducing FPRP accumulation and accumulation of lipid droplets. By co-immunohistochemical and lipid staining, greater than 99% of the cells accumulating lipid droplets possessed FPRP. FPRP mRNA and protein are also found in rat adipose tissue. Treatment of 3T3-L1 cells with an FPRP anti-sense oligonucleotide during differentiation decreased FPRP accumulation and resulted in a decrease in lipid droplets without altering the level of induction of a late marker of adipocyte differentiation, glycerol-3-phosphate dehydrogenase activity. Transient expression of an FPRP cDNA in undifferentiated 3T3-L1 cells was insufficient to induce lipid droplet accumulation.

The histone acetylase PCAF is a nuclear receptor coactivator

Whereas the histone acetylase PCAF has been suggested to be part of a coactivator complex mediating transcriptional activation by the nuclear hormone receptors, the physical and functional interactions between nuclear receptors and PCAF have remained unclear. Our efforts to clarify these relationships have revealed two novel properties of nuclear receptors. First, we demonstrate that the RXR/RAR heterodimer directly recruits PCAF from mammalian cell extracts in a ligand-dependent manner and that increased expression of PCAF leads to enhanced retinoid-responsive transcription. Second, we demonstrate that, in vitro, PCAF directly associates with the DNA-binding domain of nuclear receptors, independently of p300/CBP binding, therefore defining a novel cofactor interaction surface. Furthermore, our results show that dissociation of corepressors enables ligand-dependent PCAF binding to the receptors. This observation illuminates how a ligand-dependent receptor function can be propagated to regions outside the ligand-binding domain itself. On the basis of these observations, we suggest that PCAF may play a more central role in nuclear receptor function than previously anticipated.

BXR, an embryonic orphan nuclear receptor activated by a novel class of endogenous benzoate metabolites

Nuclear receptors are ligand-modulated transcription factors that respond to steroids, retinoids, and thyroid hormones to control development and body physiology. Orphan nuclear receptors, which lack identified ligands, provide a unique, and largely untapped, resource to discover new principles of physiologic homeostasis. We describe the isolation and characterization of the vertebrate orphan receptor, BXR, which heterodimerizes with RXR and binds high-affinity DNA sites composed of a variant thyroid hormone response element. A bioactivity-guided screen of embryonic extracts revealed that BXR is activatable by low-molecular-weight molecules with spectral patterns distinct from known nuclear receptor ligands. Mass spectrometry and 1H NMR analysis identified alkyl esters of amino and hydroxy benzoic acids as potent, stereoselective activators. In vitro cofactor association studies, along with competable binding of radiolabeled compounds, establish these molecules as bona fide ligands. Benzoates comprise a new molecular class of nuclear receptor ligand and their activity suggests that BXR may control a previously unsuspected vertebrate signaling pathway.

Localization of nascent RNA and CREB binding protein with the PML-containing nuclear body

The cellular role of the PML-containing nuclear bodies also known as ND10 or PODs remains elusive despite links to oncogenesis and viral replication. Although a potential role in transcription has been considered, direct evidence has been lacking. By developing a novel in vivo nucleic acid labeling approach, we demonstrate the existence of nascent RNA polymerase II transcripts within this nuclear body. In addition, PML and the transactivation cofactor, CREB binding protein (CBP), colocalize within the nucleus. Furthermore, we show that CBP in contrast to PML is distributed throughout the internal core of the structure. Collectively, these findings support a role for this nuclear body in transcriptional regulation.

PPARgamma promotes monocyte/macrophage differentiation and uptake of oxidized LDL

The formation of foam cells from macrophages in the arterial wall is characterized by dramatic changes in lipid metabolism, including increased expression of scavenger receptors and the uptake of oxidized low-density lipoprotein (oxLDL). We demonstrate here that the nuclear receptor PPARgamma is induced in human monocytes following exposure to oxLDL and is expressed at high levels in the foam cells of atherosclerotic lesions. Ligand activation of the PPARgamma:RXRalpha heterodimer in myelomonocytic cell lines induces changes characteristic of monocytic differentiation and promotes uptake of oxLDL through transcriptional induction of the scavenger receptor CD36. These results reveal a novel signaling pathway controlling differentiation and lipid metabolism in monocytic cells, and suggest that endogenous PPARgamma ligands may be important regulators of gene expression during atherogenesis.

Oxidized LDL regulates macrophage gene expression through ligand activation of PPARgamma

Macrophage uptake of oxidized low-density lipoprotein (oxLDL) is thought to play a central role in foam cell formation and the pathogenesis of atherosclerosis. We demonstrate here that oxLDL activates PPARgamma-dependent transcription through a novel signaling pathway involving scavenger receptor-mediated particle uptake. Moreover, we identify two of the major oxidized lipid components of oxLDL, 9-HODE and 13-HODE, as endogenous activators and ligands of PPARgamma. Our data suggest that the biologic effects of oxLDL are coordinated by two sets of receptors, one on the cell surface, which binds and internalizes the particle, and one in the nucleus, which is transcriptionally activated by its component lipids. These results suggest that PPARgamma may be a key regulator of foam cell gene expression.